WASHINGTON — EPA Administrator Lisa Jackson said Thursday she is stepping down from the Cabinet-level post after four years in which she won new federal regulations for carbon-dioxide emissions but also sparred often in bitter partisan fights with Republican lawmakers and industry executives.

Jackson, the first African American to hold the position and a chemical engineer by training, gave no signal on what she plans to do next.

But sources close to Jackson, 50, hinted she may be headed back to her former home in New Jersey, either for a chance to become president of Princeton University or to run for governor.

Reaction was largely muted among industry leaders and Republican lawmakers, as they instead viewed the opening at the Environmental Protection Agency (EPA) as a rare opportunity to push back on many regulatory policies they see as intrusive and harmful to the stumbling economy.

“Lisa Jackson and I disagreed on many issues and regulations while she headed the EPA,” said Sen. Jim Inhofe, R-Okla., senior Republican on the Senate Committee on Environment and Public Works. “However, I have always appreciated her receptivity to my concerns.”

Her leaving “provides President Obama with an opportunity to appoint an EPA administrator who appreciates the needs of our economy,” Inhofe added.

During her tenure, Jackson pressed for limits on emissions from coal-fired power plants and on dumping mining waste into streams and rivers near mines.

The slew of rules the EPA enacted in the past four years included the first greenhouse-gas standards for vehicles, cuts in mercury and other toxic pollution from power plants, and a tighter limit on soot, the nation’s most widespread deadly pollutant.

Many congressional Republicans and business groups claimed Jackson was waging a “war on coal.” But she was a hero to the environmental community.

While she successfully pushed for a number of landmark initiatives, she also suffered a high-profile setback when Obama pulled an EPA proposal last year to curb smog-forming ozone pollution. At the time, the president said the new rules would unnecessarily damage the economy and were not essential because the agency was slated to review the issue in 2013.

Obama has not picked her successor, although two leading candidates work at the EPA: Deputy Administrator Bob Perciasepe and Gina McCarthy, who heads the agency’s air and radiation office.

Perciasepe and McCarthy could face challenges in getting confirmed by the Senate because they helped craft many of the EPA’s policies during Obama’s first term. But they also are seen as career officials rather than political activists.

Other possible successors include Mary Nichols, head of the California Air Resources Board, and Kathleen McGinty, who headed the White House Council on Environmental Quality under President Clinton.

Jackson told the president after his November re-election that she no longer wanted to run the agency, and suggested she would be gone after his State of the Union address in January.

In speaking to her staff Thursday, she recalled telling Obama four years ago about the need to address climate change and other issues such as air pollution, toxic chemicals and waste-site cleanups. However, the president backed away from major climate-change efforts and other issues such as ozone pollution, leading to reports of tension between Jackson and the president. Nevertheless, Jackson said: “I leave the EPA confident the ship is sailing in the right direction.”

At the White House, Obama praised Jackson for her “unwavering commitment to the health of our families and our children.” He said she was instrumental in implementing standards to reduce mercury pollution and in implementing fuel-economy standards that will bring down gas-pump prices. “Lisa has been an important part of my team,” the president said.

Perciasepe will temporarily run the EPA.

Whomever Obama offers as a replacement, Republican lawmakers and others said they will insist on someone willing to untether industry from environmental regulations they said strangle private enterprise.

Last week, for instance, the National Association of Manufacturers decried new regulations requiring industrial, commercial and institutional boilers across the nation to meet new emission limits and work-practice standards.

Many in the environmental field praised Jackson.

S. William Becker, executive director of the National Association of Clean Air Agencies, called her “an extraordinary leader.” Frances Beinecke, president of the Natural Resources Defense Council, said there was “no fiercer champion of our health and our environment.”